x-bar chart.R

# Import the qcc library
library(qcc)

# Create a measures column
measures <- rnorm(200, 3, 1)

# Specify the sample size
sample_size <- 5

# Get the total number of samples
number_of_samples <- length(measures)/sample_size

# Assign the measures to the corresponding sample
sample <- rep(1:number_of_samples, each = sample_size)

# Create a data frame with the measures and sample columns
df <- data.frame(measures, sample)

# Group the measures per sample
measure <- with(df, qcc.groups(measures, sample))

# View the grouped measures
head(measure)

# Specify the measures unit
measure_unit <- "lbs"  

# Create the x-bar chart
xbar <- qcc(measure, type = "xbar", data.name = measure_unit)

# Specify the warning limits (2 sigmas)
(warn.limits.2 = limits.xbar(xbar$center, xbar$std.dev, xbar$sizes, 2))

# Specify the warning limits (1 sigmas)
(warn.limits.1 = limits.xbar(xbar$center, xbar$std.dev, xbar$sizes, 1))

# Plot the x-bar chart
plot(xbar, restore.par = FALSE)

# Plot the warning limit lines
abline(h = warn.limits.2, lty = 2, col = "blue")
abline(h = warn.limits.1, lty = 2, col = "lightblue")

# Get the summary for x-bar chart
summary(xbar)